The present invention relates a transmission mechanism, and more particularly to a bi-power transmission mechanism practical for use in any of a variety of blinds, precision machinery and instruments, which comprises two power inputs and one power output.
Conventional Venetian blinds include two types, namely, the horizontal type and the vertical type. A regular horizontal blind uses a transmission rod to tilt slats horizontally. A regular vertical blind uses a transmission rod to tilt slats vertically. In a roller blind, a transmission rod is driven to take up or let off blind cloth. The transmission rod of a blind may be driven manually, or by a power unit. A manually operated blind must be operated by hand. It is inconvenient to some people, for example, patients or disabled persons to operate a manually operated blind. A power-driven blind can easily be operated. However, a power-driven blind cannot work when its circuit or the electric power fails. Therefore, there is a strong demand for a bi-power transmission mechanism that enables a blind to be optionally operated by electricity or the hand.
The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a bi-power transmission mechanism, which is practical for use in blinds, mechanical arms, small machines, and etc. that can be optionally operated by electricity, or the hand. It is another object of the present invention to provide a bi-power transmission mechanism, which is practical for use in a precision machine or instrument that needs to regulate the speed automatically, or requires feedback compensation. According to one aspect of the present invention, the bi-power transmission mechanism comprises a first power unit, a second power unit, and a planetary gear train. The first power unit comprises a motor, an input shaft, a worm, and a worm gear driven by the motor through the worm to rotate the input shaft. The planetary gear train comprises a center gear synchronously rotated with the input shaft of the first power unit, a rack, a plurality planet gears equiangularly supported on the rack and meshed with the center gear, and an output shaft fixedly mounted on the rack for synchronous rotation with the rack and the input shaft of the first power unit. The second power unit is operated to rotate the planet gears through an internal gear via a worm and a worm gear so as to further rotate the output shaft of the planetary gear train when the first power unit fails to function well. In one embodiment of the present invention, the second power unit is operated by electricity. In another embodiment of the present invention, the second power unit is manually operated.